Hydraulic system

ABSTRACT

The invention concerns a hydraulic system comprising at least one hydraulic drive means ( 1 ), a conduit system ( 10 ) connected to the hydraulic drive means for conveying hydraulic liquid to and from the hydraulic drive means, where the conduit system comprises a conduit circuit ( 11 ) containing hydraulic liquid, connected to the hydraulic drive means, a pump ( 12 ) for generating a flow of hydraulic fluid in the conduit system and a motor ( 13 ) to power the pump. The pump ( 12 ) is arranged to control the flow of hydraulic liquid in said circuit ( 11 ), and the hydraulic drive means ( 1 ) is controllable substantially only by controlling the flow of hydraulic liquid in said circuit ( 11 ) by means of the pump ( 12 ).

FIELD OF THE INVENTION AND PRIOR ART

The invention concerns a hydraulic system, comprising at least onehydraulic drive means, a conduit system connected to the hydraulic drivemeans for conveying hydraulic liquid to and from the hydraulic drivemeans, where the conduit system comprises a conduit circuit containinghydraulic liquid, connected to the hydraulic drive means, a pump forgenerating a flow of hydraulic fluid in the conduit system and a motorto power the pump.

Hydraulic systems of the type mentioned in the introduction are knownand are used in a large number of different technical fields. Forexample one or more hydraulic cylinders in such a hydraulic system canbe used in an industrial truck to control its lifting movements, i.e.control of the truck's handling of a load including raising and loweringthe load, and even horizontal movements of the load. Further examples oftechnical fields where the said type of hydraulic system can be appliedinclude all sorts of working machines, such as digging machines forcontrol of the digging machine's digging movements, tool machines,robots and such for example.

In hydraulic systems of the said type the motor's power is transformedto hydraulic power in the pump, whereby the flow of hydraulic liquid inthe conduit system generated by the pump is usually distributed to theat least one hydraulic drive means via one or more valves. Bycontrolling the flow to at least one hydraulic drive means via valves,such as throttle valves or directional valves for example, the hydraulicdrive means is thereby controlled. However, a disadvantage with such ahydraulic system is that heat is generated on controlling the flow withthrottle valves, which has a negative effect on the components comprisedin the system and therefore the installation of expensive coolingsystems requires in certain cases. The generation of heat also involvesa disadvantageous energy loss.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide therefore a hydraulicsystem that allows a more effective utilisation of the energy consumedthan in hydraulic systems according to the prior art.

This aim is achieved according to the invention with a hydraulic systemof the type mentioned in the introduction, in which the pump is arrangedto control the flow of hydraulic liquid in said circuit, and thehydraulic drive means is controllable substantially only by controllingthe flow of hydraulic liquid in said circuit by means of the pump.

Due to the fact that the hydraulic drive means is controllablesubstantially only by controlling the flow of hydraulic fluid in saidcircuit by means of the pump, the generation of heat and the energy lossthat is associated with controlling the hydraulic drive means bythrottling the flow of hydraulic liquid in the conduit system withvalves is avoided. Furthermore the pump only has to be powered at thosetimes when the hydraulic drive means is to be operated, whichcontributes to a reduced energy consumption in the hydraulic system.Furthermore the pump's work is related to the control of the hydraulicdrive means. For example a smaller movement of the hydraulic drive meansin the form of a hydraulic cylinder requires less work by the pump, oncondition that the load on the hydraulic cylinder is not changed. Theinventive hydraulic system even allows the use of a reduced amount ofhydraulic liquid compared with hydraulic systems according to the priorart, because the control of the hydraulic drive means only requirescontrol of the flow of hydraulic liquid in the conduit circuit connectedto the hydraulic drive means, i.e. no superfluous flow of hydraulicliquid needs to be circulated through the conduit system to maintain thedesired control of the hydraulic drive means.

According to a preferred embodiment of the invention the hydraulicsystem comprises means for regenerating mechanical energy transmitted tothe hydraulic drive means, due to loading of the hydraulic drive means.It is hereby possible to regenerate energy that is transferred to thehydraulic drive means due to loading of the hydraulic drive means, whichcan then be utilised in any way.

According to another preferred embodiment of the invention said energyregeneration means include the motor, that is arranged to be driven as agenerator by the pump, for regeneration of energy when said mechanicalenergy transmitted to the hydraulic drive means is transformed to liquidenergy in the hydraulic liquid in said circuit and thereby powers thepump. The motor is therefore arranged to both power the pump to controlthe flow of hydraulic liquid in said circuit and thereby control thehydraulic drive means and to work as generator for regeneration ofenergy obtained from the hydraulic drive means. No further devices forthe regeneration of energy are therefore required.

According to another preferred embodiment of the invention the motor ispowered by energy regenerated by said energy regeneration means. Areduced energy consumption by the hydraulic system is consequently madepossible in an advantageous way.

Further advantages, advantageous features and areas of application forthe invention will be apparent from the other dependent claims and thefollowing description.

BRIEF DESCRIPTION OF THE DRAWING

Preferred embodiments of the invention are described below as exampleswith reference to the attached drawing, in which:

FIG. 1 schematically illustrates a hydraulic system according to apreferred embodiment of the invention.

DETAILED, DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 schematically illustrates a hydraulic system according to apreferred embodiment of the invention. The hydraulic system illustratedin FIG. 1 comprises a hydraulic drive means in the form of a hydrauliccylinder 1. It is pointed out that this is only a possible embodimentand it is of course possible to provide the hydraulic system with anoptional number of hydraulic cylinders, depending on the task that thehydraulic system is intended to carry out. Furthermore it is pointed outthat it is even possible to use many other types of hydraulic drivemeans, such as different types of hydraulic adjusting devices andhydraulic motors for example.

A conduit system, schematically shown by 10, is connected with thehydraulic cylinder to convey hydraulic liquid to and from the hydrauliccylinder 1. A suitable choice of hydraulic liquid is easy for a personskilled in the art to make, so it will not be discussed any further. Theconduit system 10 comprises a conduit circuit 11 containing hydraulicfluid connected to the hydraulic cylinder 1. Furthermore the hydraulicsystem comprises a pump 12 to generate a flow of hydraulic liquid in theconduit system and a motor 13 to power the pump 12. Although the pump 12and the motor 13 in FIG. 1 are illustrated as separate components it isto be understood that these could be arranged in one and the same unitconstituting one component.

The pump 12 is arranged to control the flow of hydraulic liquid in saidcircuit 11 and the hydraulic cylinder 1 is controllable substantiallyonly by controlling the flow of hydraulic liquid in said circuit 11 bymeans of the pump 12. The control of the hydraulic cylinder 1 thereforetakes place substantially only by controlling the flow of hydraulicliquid in circuit 11 by means of the pump 12 and consequently not bycontrolling the flow to and from the hydraulic cylinder by means of anyvalves.

The hydraulic cylinder 1 illustrated in FIG. 1 comprises a piston 2,with which a piston rod is connected. The piston 2 divides the hydrauliccylinder into two separated chambers, namely a first chamber 4 and asecond chamber 5. The piston 2 and the piston rod 3 are movable back andforth in the hydraulic cylinder 1. The circuit 11 has a connection tothe first chamber 4 and a connection to the second chamber 5.

The pump 12 is preferably arranged to control the direction of the flowof hydraulic liquid in the circuit 11 and thereby to control thedirection of action of the hydraulic cylinder 1, i.e. the direction inwhich the piston 2 and the piston rod 3 will move. By controlling thedirection of the flow of hydraulic liquid in circuit 11 the piston 2,and therefore the piston rod 3, can therefore be made to move in thedirections shown by the bi-directional arrow I. The flow of hydraulicliquid in one of the two directions in the circuit 11 is thereforegenerated by means of the pump 12, whereby a higher pressure isgenerated either in the first chamber 4 or in the second chamber 5,depending on the chosen flow direction of the hydraulic liquid in thecircuit 11, which pushes the piston 2 in the chosen direction of thebi-directional arrow I.

The pump 12 is preferably arranged to control the flow rate of hydraulicliquid in the circuit 11 and thereby to control the direction of actionof the hydraulic cylinder 1, i.e. the rate at which the piston 2 and thepiston rod 3 move in one of the two directions according to thebi-directional arrow I.

According to the embodiment of the invention illustrated in FIG. 1 themotor 13, which powers the pump 12, is arranged to control the pump tocontrol the flow of hydraulic liquid in the circuit 11. The flow in thecircuit 11 is therefore controlled by controlling the motor. For examplethe motor 13 can be arranged so that at high motor revolutions the pump12 is made to generate a high flow rate in the circuit 11 and at lowmotor revolutions the pump 12 is made to generate a low flow rate in thecircuit 11 respectively. The motor 13 can even be arranged so that athigh motor revolutions the pump 12 is made to generate a high pressurein the hydraulic liquid on one side of the pump 12 in the circuit 11 andthat at reduced high motor revolutions the pump 12 is made to generate areduced high pressure in the hydraulic liquid on one side of the pump 12in the circuit 11.

In the embodiment of the invention illustrated in FIG. 1 a device 14 isconnected to the motor 13 to power and control the motor 13, which inturn is arranged to control the pump 12. The device 14 suitablycomprises a connection to an energy source to power the motor 13.According to the illustrated embodiment of the invention the motor 13 iselectrically powered. The device 14 can for example be connected to anelectricity network, but according to this embodiment of the inventionbatteries, preferably rechargeable batteries, are arranged in the device14 to power the motor 13. It is of course also possible to arrange themotor 13 to be powered in some other way. The motor 13 could for examplebe petrol- or diesel-powered.

In the embodiment of the invention illustrated in FIG. 1 the hydrauliccylinder 1 is intended to move a beam 6 that is arranged on anindustrial truck for lifting and lowering a load for example. It isemphasized that this example is only cited to explain the invention andshould not be interpreted as limiting the present invention. The end 8of hydraulic cylinder's 1 piston rod 3 which is opposite to the piston 2is pivotably connected to the beam 6 via an attachment. By controllingthe hydraulic cylinder 1 by means of the pump 12 and thereby displacingthe piston 2 and the piston rod 3 in the direction of the arrow I, thebeam 6, which is pivotable about a pivoting axis 7 can be brought topivot in the direction of the bi-directional arrow II.

The hydraulic system preferably comprises means for regeneratingmechanical energy transmitted to the hydraulic cylinder 1, due toloading of the hydraulic cylinder 1.

On pivoting the beam 6 in the upward direction in FIG. 1 energy istransferred from the hydraulic cylinder 1 to the beam 6. By pivoting thebeam gains a higher potential energy. Said energy regeneration means isintended to regenerate mechanical energy that is transferred to thehydraulic cylinder, such as for example by lowering the beam 6 when thebeam's potential energy and mechanical energy from another loading ofthe beam is transferred to the hydraulic cylinder 1. Many types ofenergy regeneration means are possible within the scope of theinvention. For example it would be possible to arrange resilient membersto take up, and later use the mechanical energy transferred to thehydraulic cylinder 1.

According to the embodiment of the invention illustrated in FIG. 1 saidenergy regeneration means includes the motor 13. The motor is arrangedto be driven as a generator by the pump 12. On loading of the hydrauliccylinder, such as for example by the beam 6, the mechanical energy istransferred to the hydraulic cylinder 1, where the energy is transformedinto liquid energy in the hydraulic liquid in the circuit 11 by thepiston 2 of said load being pushed in one of the two directions of thebi-directional arrow I. In this way a flow of hydraulic liquid in thecircuit is generated, which powers the pump 12, which in turn powers themotor 13 as a generator for regenerating the mechanical energytransferred to the hydraulic cylinder.

The hydraulic system preferably even comprises means to storeregenerated energy. Such energy storage means can include capacitors,different types of accumulators and such. According to the illustratedembodiment of the invention said energy storage means comprises one ormore rechargeable batteries arranged in the device 14.

The motor 13 is suitably arranged to be powered by the energyregenerated by said energy regeneration means, which for example can bestored in said energy storage means. This makes a reduction in totalenergy needed to power the motor possible, which is particularlyadvantageous in cases where the motor 13 is arranged to be powered bybatteries.

The volume of hydraulic liquid in the hydraulic cylinder's 1 firstchamber 4 when the piston is located in one of its end positions, theend position to the right in FIG. 1, is larger than the volume ofhydraulic liquid in the hydraulic cylinder when the piston 2 is locatedin its other end position, the end position to the left as illustratedin FIG. 1. The difference between these two volumes is substantially thevolume of the piston rod 3 in the second chamber 5. Due to this, thehydraulic liquid has to be supplied or removed from the circuit 11 whenthe hydraulic cylinder is controlled so that the piston moves inside thehydraulic cylinder 1. Three conduits 20, 21 and 22 are connected to thecircuit 11 to supply and remove hydraulic liquid, where the conduits areeven connected to a tank for hydraulic liquid, schematically indicatedby 19. In order to control the flow of hydraulic liquid between the tank19 and the circuit 11, valves 16, 17, 18 are arranged in the conduits20, 21, 22. A valve 16 is arranged in the conduit 20. A valve 18 isarranged in the conduit 22, which in the illustrated embodiment is aso-called one-way valve, i.e. the valve 18 transmits hydraulic liquid inonly one direction, which in FIG. 1 is indicated by the arrow III.Furthermore a valve 17 is even arranged in conduit 21.

Furthermore a valve 15 is arranged in circuit 11, which is arranged tobe closed and thereby not allow any flow of hydraulic liquid in thecircuit 11 when the hydraulic cylinder 1 should not move. On controllingthe hydraulic cylinder 1 the valve 15 consequently opens to allow flowof hydraulic liquid in the circuit 11. Lacking such a valve, whichprevents flow in circuit 11 in closed position, the load on thehydraulic cylinder via the piston rod 3 would not encounter anyresistance, whereby the piston rod 3 and the piston 2 would be able tomove in the direction of the arrow I on generation of a flow in thecircuit 11. The valve 15 in its closed position is therefore intended tofix the hydraulic cylinder's piston and piston rod in a determinedposition independently of the amount of load on the hydraulic cylinder.

There now follows a brief description of the function of the hydraulicsystem in operation according to the embodiment of the inventionillustrated in FIG. 1.

When the hydraulic cylinder 1 is to be controlled so that the piston 2and the piston rod 3 move to the right in FIG. 1, i.e. on raising thebeam 6, the pump 12 is controlled by the motor 13 that generates a flowof the hydraulic liquid in the circuit 11 in a clockwise direction. Thevalves 16 and 17 are hereby kept closed, i.e. no flow of hydraulicliquid is allowed between the tank 19 and the circuit 11 via theconduits 20 and 21. The extra volume of hydraulic liquid which is neededto be supplied to the circuit 11 corresponding to the volume taken up bythe piston rod 3 in the hydraulic cylinder 1 is automatically sucked upfrom the tank by conduit 22 via the one-way valve 18.

On lowering the beam 6, in other words when the hydraulic cylinder 1 isto be controlled so that the piston 2 and the piston rod 3 move to theleft in FIG. 1, the valve 15 is opened so that a flow of hydraulicliquid in the circuit 11 is allowed. The mass of the beam 6 and any loadon the beam 6, for example the load carried thereupon, load thehydraulic cylinder 1, i.e. push the piston rod 3 to the left in FIG. 1along the direction of the arrow I, whereby a flow is generated in thehydraulic liquid in the circuit 11 in the anti-clockwise direction. Thisflow powers the pump 12, which in turn powers the motor 13 which isthereby driven as a generator for regeneration of energy according tothe above description. In this way an advantageous utilisation of themechanical energy which is transferred to the hydraulic cylinder 1 isconsequently possible. The regenerated energy can for example be used torecharge the batteries arranged in the device 14 for powering the motor13. In cases where battery power is utilised such energy regenerationincreases the lifetime of the batteries. In the case of a battery-drivenvehicle, for example, the energy regeneration results in a longerdrive-time between battery charging and a reduction of the risk ofinvoluntary interruption of a work shift in order to charge thebatteries.

The flow rate in the circuit 11 on energy regeneration, and thereby therate of lowering the beam 6, is controlled by powering the motor 13 sothat the pump 12 slows down the anti-clockwise flow in the circuit 11,which is generated by the load on the hydraulic cylinder. Thesuperfluous volume of hydraulic liquid due to the volume of the pistonrod 3 which, in connection with the flow in the circuit 11 onregeneration of energy, has to be removed from the circuit 11 is insteadtapped off by conduit 11 by opening the valve 17.

When the beam is to be lowered further than its position due to its massand any load on the beam 6, i.e. when the piston 2 and the piston rod 3are to be moved further to the left in FIG. 1, the pump has to activelygenerate a flow in the circuit 11 to control the hydraulic cylinder.This occurs for example when it is desired to forcibly press down thebeam 6. In order for the hydraulic liquid not to then be forced out intothe tank 19 via conduit 21 the valve 17 is closed. The superfluousvolume of hydraulic liquid due to the piston rod's 3 volume, which is tobe removed from the circuit 11, is instead tapped off via conduits 20 byopening the valve 16.

The invention is of course not in any way limited to the preferredembodiments described above, but a number of modification possibilitiesthereof should be apparent for the average person skilled in the artwithout departing from the basic idea of the invention, as defined inthe attached claims.

1. Hydraulic system, comprising at lest one hydraulic drive means (1), aconduit system (10) connected to the hydraulic drive means for conveyinghydraulic liquid to and from the hydraulic drive means, where theconduit system comprises a conduit circuit (11) containing hydraulicliquid, connected to the hydraulic drive means, a pump (12) forgenerating a flow of hydraulic fluid in the conduit system and a motor(13) to power the pump, wherein the pump (12) is arranged to control theflow of hydraulic liquid in said circuit (11), and the hydraulic drivemeans (1) is controllable substantially only by controlling the flow ofhydraulic liquid in said circuit (11) by means of the pump (12). 2.Hydraulic system according to claim 1, wherein the pump (12) is arrangedto control direction of the flow of hydraulic liquid in said circuit(11) and thereby control the direction of action of the hydraulic drivemeans (1).
 3. Hydraulic system according to claim 1, wherein the pump(12) is arranged to control the flow rate of the hydraulic liquid insaid circuit (11) and thereby control the effective rate of thehydraulic drive means (1).
 4. Hydraulic system according to claim 1,wherein the motor (13), that powers the pump (12), is arranged tocontrol the pump to control the flow of hydraulic liquid in said circuit(11).
 5. Hydraulic system according to claim 1, wherein said motor (13)is an electrically driven motor.
 6. Hydraulic system according to claim1, wherein it comprises means for regenerating mechanical energytransmitted to the hydraulic drive means (1), due to loading of thehydraulic drive means.
 7. Hydraulic system according to claim 6, whereinsaid energy regeneration means include the motor (13), that is arrangedto be driven as a generator by the pump (12), for regeneration of energywhen said mechanical energy transmitted to the hydraulic drive means (1)is transformed to liquid energy of the hydraulic liquid in said circuit(11) and thereby powers the pump (12).
 8. Hydraulic system according toclaim 6, wherein it comprises means to store regenerated energy. 9.Hydraulic system according to claim 8, wherein said energy storage meanscomprises at least one rechargeable battery.
 10. Hydraulic systemaccording to claim 6, wherein the motor (13) is powered by the energyregenerated by said energy regenerated means.
 11. Hydraulic systemaccording to claim 10, wherein the motor (13) is powered by regeneratedenergy stored in said energy storage means.
 12. Hydraulic systemaccording to claim 1, wherein the hydraulic drive means (1) is ahydraulic cylinder.
 13. Hydraulic system according to claim 12, whereinthe hydraulic cylinder has chambers (4, 5) containing hydraulic liquid,arranged on opposite sides of a piston (2), with a piston rod (3)connected to the piston received in one chamber (5), and the systemcomprises an arrangement (16-22) arranged to provide a supply ofhydraulic liquid to said conduit circuit (11) on controlling thehydraulic cylinder (1) to move the piston in a direction for reducingthe volume of said one chamber (5) and to tap hydraulic liquid from theconduit circuit (11) on movement of the piston in the oppositedirection.
 14. Hydraulic system according to claim 13, wherein thearrangement comprises at least two conduits connected to a tank (19) forhydraulic liquid and to the conduit circuit (11) via a valve (17, 18)each.
 15. Hydraulic system according to claim 14, wherein a first of theconduits connected to the hydraulic liquid tank has a one-way valve (18)that only makes the flow of hydraulic liquid from the tank (19) to theconduit circuit (11) possible to supply hydraulic liquid to the conduitcircuit on movement of the piston in the direction for reducing thevolume in said one chamber (5) when the valve (17) is closed in thesecond conduit (21) to the tank, whereby the second conduit is connectedto the conduit circuit (11) nearer to said one chamber (5) than to thefirst conduit (22).
 16. Hydraulic system according to claim 15, whereinthe valve (17) in the second conduit (21) is controllable to be openwhen the piston is displaced in the direction for reducing the volume insaid one chamber (5).
 17. Hydraulic system according to claim 15,wherein the arrangement comprises a third conduit (20) connected, via avalve (16), to the hydraulic liquid tank (19) which is connected to theconduit circuit (11) on the opposite side of the first conduit's (22)connection thereto relative to the second conduit (21), and the valve(17) in the second conduit (21) is controllable to be closed and thevalve (16) in the third conduit (20) is controllable to be opensimultaneously when the piston is displaced in the direction forreducing the volume in said one chamber (5).
 18. Hydraulic systemaccording to claim 2, wherein the pump (12) is arranged to control theflow rate of the hydraulic liquid in said circuit (11) and therebycontrol the effective rate of the hydraulic drive means (1). 19.Hydraulic system according to claim 7, wherein it comprises means tostore regenerated energy.
 20. Hydraulic system according to claim 16,wherein the arrangement comprises a third conduit (20) connected, via avalve (16), to the hydraulic liquid tank (19) which is connected to theconduit circuit (11) on the opposite side of the first conduit's (22)connection thereto relative to the second conduit (21), and the valve(17) in the second conduit (21) is controllable to be closed and thevalve (16) in the third conduit (20) is controllable to be opensimultaneously when the piston is displaced in the direction forreducing the volume in said one chamber (5).